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No. 232 - Start of Eclipse Season; Completion of Radio Science Investigations Occultation Campaign #10

No. 232 - Start of Eclipse Season; Completion of Radio Science Investigations Occultation Campaign #10

Report for the period 27 February to 26 March 2011 (week 9 - week 12)The reporting period, covering four weeks of Venus Express mission operations, was devoted to routine science activities. Twelve occultations were observed for Radio Science Investigations (RSI) campaign #10.

Eclipse season

An eclipse season started on 13 March 2011; in preparation for this, the end-of-charge setting for the battery was returned to 100% on 11 March 2011. During eclipse seasons, Venus Express passes through the shadow of Venus during parts of its orbit around the planet; the resulting thermal control and power requirements lead to increased demands being placed on the spacecraft’s batteries.

VeRa Earth occultation campaign #10

The mission's tenth Earth occultation campaign was completed during this reporting period. These campaigns take place when the Earth is occulted by the disk of Venus; this occurs around the pericentre passages as seen from the spacecraft. Under these conditions unique measurements can be made to investigate the fine structure of the neutral atmosphere and ionosphere of Venus.

The occultation measurements are part of the Venus Express Radio Science Investigations (RSI) performed under the Venus Radio Science experiment (VeRa). For these investigations the VeRa team makes use of the radio links of the spacecraft's communications system. The spacecraft's High Gain Antenna (HGA) is pointed toward the Earth before the approach to occultation. The on-board ultra-stable oscillator is used to generate a very stable signal which is sent to Earth over the HGA simultaneously in the S-band and X-band. Just before and after the occultation the transmitted radio signal passes through the ionosphere and atmosphere of Venus. The effect that this has on the received signal gives valuable information on the characteristics of the atmosphere (such as temperature, density and pressure) as a function of altitude.

RSI occultation measurements were performed around pericentre on twelve orbits in the reporting period. Two ground stations were used for receiving the spacecraft's radio signals on ground: the ESA deep space antenna at New Norcia (NNO) and the NASA Deep Space Network ground station at Canberra (CAN).

Summary of main activities

During the reporting period, routine mission operations were conducted using the ESA Cebreros ground station (CEB). Delta Differential One-way Ranging (DDOR) was performed on 20 March 2011, using the New Norcia (NNO) ground station. RSI measurements were performed by observing the occultation of signals from the Venus Express spacecraft as it passed through orbital pericentre. A total of twelve observations were performed, using the NASA Deep Space Network Canberra (CAN) and ESA New Norcia ground stations. RSI Occultation Campaign #10 ended on 23 March 2011.

Bad weather at the Cebreros ground station caused the data downlink on 4 March 2011 to be interrupted. Some Venus Monitoring Camera (VMC) data were lost; all other science data were downloaded during subsequent communications passes.

Venus Express has two star trackers, which are used by the spacecraft control system to maintain knowledge of the spacecraft attitude in space. On 07 March 2011, there was an interruption of communications between the main star tracker A and the spacecraft control software. This is not common, but has occurred in the past. The power to the star tracker was cycled (off, then on), the software re-started correctly and the communications were restored. The cause of the communication problem is not known, but the brief communication breaks are not considered serious.

Main activities during reporting period

MET
(Day)

Date
(DD-MON-YYYY)

DOY

Main Activity

MET = Mission elapsed time; DOY = Day of year

1937 27-Feb-2011 58 RSI occultation over NNO around pericentre. CEB communications pass.
1938 28-Feb-2011 59 CEB communications pass.
1939 1-Mar-2011 60 RSI occultation over NNO around pericentre. CEB communications pass.
1940 2-Mar-2011 61 CEB communications pass.
1941 3-Mar-2011 62 RSI occultation over NNO around pericentre. CEB communications pass.
1942 4-Mar-2011 63 CEB communications pass.
1943 5-Mar-2011 64 RSI occultation over CAN around pericentre. CEB communications pass.
1944 6-Mar-2011 65 CEB communications pass.
1945 7-Mar-2011 66 RSI occultation over NNO around pericentre. CEB communications pass. Star Tracker A power reset.
1946 8-Mar-2011 67 CEB communications pass shortened due to maintenance from 11:00 to 16:00.
1947 9-Mar-2011 68 CEB communications pass shortened due to maintenance from 11:00 to 16:00.
1948 10-Mar-2011 69 RSI occultation over CAN around pericentre. CEB communications pass.
1949 11-Mar-2011 70 CEB communications pass.
1950 12-Mar-2011 71 CEB communications pass.
1951 13-Mar-2011 72 CEB communications pass.
1952 14-Mar-2011 73 RSI occultation over CAN around pericentre. CEB communications pass. Telemetry bit rate decreased to 152 kbps.
1953 15-Mar-2011 74 CEB communications pass.
1954 16-Mar-2011 75 RSI occultation over NNO around pericentre. CEB communications pass.
1955 17-Mar-2011 76 CEB communications pass.
1956 18-Mar-2011 77 RSI occultation over NNO around pericentre. CEB communications pass.
1957 19-Mar-2011 78 CEB communications pass.
1958 20-Mar-2011 79 DDOR with NNO just before CEB pass. CEB data was lost due to ground hardware failure, so DDOR was unsuccessful. CEB communications pass.
1959 21-Mar-2011 80 RSI occultation over CAN around pericentre. CEB communications pass.
1960 22-Mar-2011 81 RSI occultation over CAN around pericentre. CEB communications pass.
1961 23-Mar-2011 82 RSI occultation over NNO around pericentre. CEB communications pass.
1962 24-Mar-2011 83 CEB communications pass.
1963 25-Mar-2011 84 CEB communications pass.
1964 26-Mar-2011 85 CEB communications pass.

At the end of the reporting period on 26 March 2011, Venus Express was 183.4 million kilometres from Earth. The one-way signal travel time was 611 seconds.

At the end of the reporting period, the final oxidizer mass was estimated to be 34.496 kilograms, and the final fuel mass estimate was 21.537 kilograms.

Payload Activities

ASPERA The instrument was regularly operated as part of the routine plan.
MAG The instrument was regularly operated as part of the routine plan.
PFS The instrument was not operated.
SPICAV The instrument was regularly operated as part of the routine plan.
VMC The instrument was regularly operated as part of the routine plan.
VeRa Radio Science Investigation (RSI) occultation experiments were carried out via New Norcia (seven passes) and NASA DSN Canberra (five passes).
VIRTIS The instrument was regularly operated as part of the routine plan.

Future Milestones

Atmospheric Drag Experiment (ADE) #5 will start on 23 May 2011. Superior solar conjunction will start on 6 August 2011.


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This report is based on four ESOC mission operations reports, MOR #277 through MOR #280. Please see the copyright section of the legal disclaimer (bottom of this page) for terms of use.

Last Update: 1 September 2019
30-Nov-2021 17:52 UT

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